Most interface motion goes unnoticed, and that is the goal. When a menu opens from the button you pressed, or a toast leaves the way it came in, nobody stops to admire it. They simply understand what happened and carry on. Good motion answers a question before the user thinks to ask it.

Bad motion is the opposite. It asks for attention it has not earned. A dialog that takes half a second to appear feels slow even when the network is instant, and a list that staggers in on every visit turns a quick glance into a small wait. The cost is paid every single time the thing happens.

Start from frequency

The first question is how often someone will see an animation. Something used a hundred times a day, like a command palette, should appear at once. Something seen a few times a day, like a drawer or a modal, can take around two hundred milliseconds. Something rare, like finishing onboarding, has room for a little delight.

Easing matters as much as duration. An ease-out curve moves quickly at the start, so the interface responds the moment you act, then settles gently. An ease-in curve does the reverse and feels sluggish, because the slow part lands exactly when you are watching most closely.

Motion as explanation

The best animations explain structure. A panel that slides in from the right tells you it can be dismissed by sliding it back. A highlight that glides between tabs tells you the tabs belong together. Change the element without motion and you lose that small lesson about how the interface is built.

Finally, motion should always be interruptible. People change their minds mid-gesture, click twice, or press Escape halfway through an opening. Transitions and springs can reverse from wherever they are; fixed keyframes restart from zero and feel broken. Build for the interruption and the rest tends to follow.